The general consensus is that one of these two teams will finish as runners-up to Brazil in Group E.
Serbia began perfectly: a 1-0 win over Costa Rica, thanks to a stunning Aleksandar Kolarov free kick, put them in a strong position with two games left to play.
Switzerland, meanwhile, were impressive in a game many expected them to lose heavily. A resolute defensive performance kept Brazil at bay and set things up nicely for a potentially decisive clash with Serbia.
The onus will be on Switzerland to take the game to Serbia although the game is unlikely to be an open and expansive one.
In a game that could decide who progresses into the Round of 16, here are three key battles to look out for: